Video images are configured from successive still images, and there is generally a need to code video images in video image transmission due to the large data volume. Coding video images is coding processing that converts one video image data stream into another data stream, and is called compression processing that compresses the video image data volume. Due to enabling the compression of large data volume video images, video coding technology has become indispensable in terrestrial digital broadcasting, Blu-ray (registered trademark), and for transmitting and recording movies with digital cameras. H.264/AVC is an example of a typical video coding method standard. High Efficiency Video Coding (HEVC) is also planned to become a standard as a next generation video coding technology, and has a coding efficiency that is two times that of H.264/AVC or greater.
Note that known video coding methods include inter prediction coding methods (also referred to as inter-frame prediction coding methods) and intra prediction coding methods (also referred to as in-frame prediction coding methods).
Inter prediction coding methods utilize a high correlation (high degree of similarity) of video images in the time direction, and perform coding of frame images of coding targets by comparing a decoded image decoded from an already coded frame image, in order to remove redundancy.
Intra prediction coding methods utilize a high correlation of video image in the spatial direction, and code a frame image of a coding target using only data within the coding target frame image, and without employing other frame images. Specifically, a predicted image is generated of a coding target block contained in a frame image by using reference pixels at peripheral blocks to the coding target block, and a difference between the predicted image and an original image is coded.
There is a need to select a prediction mode for use when generating a predicted image to improve the coding efficiency using an intra prediction coding method. A predicted image generated using the optimal prediction mode has a small difference to the original image and good coding efficiency. For example, when coding a luma signal using the HEVC method that is planned to become a standard, an optimal prediction mode is selected from 35 types of prediction mode as illustrated in FIG. 4, and the predicted image is generated.
Up to now, in order to select the optimal prediction mode, predicted images are generated for prediction mode determination from reference pixels of peripheral blocks of the coding target block for all of the prediction modes, and coding costs thereof are computed. Then, the prediction mode with the minimum coding cost is selected as the optimal prediction mode by comparison of all the coding costs. The computation and comparison of coding cost is referred to below as coding cost evaluation.
[Related Non-Patent Documents]
High efficiency video coding (HEVC) text specification draft 6, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 7th Meeting: Geneva, CH, 21-30 Nov., 2011.